[ORC] SimpleRemoteEPCServer: exit gracefully when detecting invalid connection

[sgraenitz]

Summary

In case of invalid connectivity settings, EPC transport's listenLoop() thread may tear down the server. In this case, the main thread won't reach the waitForDisconnect() in the main function and instead exit via ExitOnErr before. The server's ShutdownErr member will still hold an unchecked error, which causes an abnormal shutdown:

SimpleRemoteEPCServer::sendMessage: opc = Setup, seqno = 0, tag-addr = 0x0, arg-buffer = 0x48c bytes
  \--> SimpleRemoteEPC::sendMessage failed
Program aborted due to an unhandled Error:
Bad file descriptor

Call-stack of the main thread:

abort()
llvm::Error::fatalUncheckedError() const
llvm::Error::assertIsChecked()
llvm::Error::~Error()
llvm::orc::SimpleRemoteEPCServer::~SimpleRemoteEPCServer()
...
llvm::Expected<...> llvm::orc::SimpleRemoteEPCServer::Create<...>(...)
main

With this patch applied, the server will shutdown gracefully:

SimpleRemoteEPCServer::sendMessage: opc = Setup, seqno = 0, tag-addr = 0x0, arg-buffer = 0x48c bytes
  \--> SimpleRemoteEPC::sendMessage failed
SimpleRemoteEPCServer: Bad file descriptor
llvm-jitlink-executor: Bad file descriptor

The duplicate error message appears to be originating from the two threads involved.

[sgraenitz]

I can't reproduce the original error on mainline anymore. I guess one of the EPC refactors fixed the issue on the way. Thanks

llvm/include/llvm/ExecutionEngine/Orc/TargetProcess/SimpleRemoteEPCServer.h

Create(unique_function<Error(Setup &S)> SetupFunction,
     Setup S(*Server);
     if (auto Err = SetupFunction(S))
       return std::move(Err);
 
     // Set ReportError up-front so that it can be used if construction
     // process fails.
     if (!Server->ReportError)
       Server->ReportError = [](Error Err) {
-        logAllUnhandledErrors(std::move(Err), errs(), "SimpleRemoteEPCServer ");
+        logAllUnhandledErrors(std::move(Err), errs(),
+                              "SimpleRemoteEPCServer: ");
       };
 
     // Attempt to create transport.
     auto T = TransportT::Create(
         *Server, std::forward<TransportTCtorArgTs>(TransportTCtorArgs)...);
     if (!T)
       return T.takeError();
     Server->T = std::move(*T);
#endif
   Expected<HandleMessageAction>
   handleMessage(SimpleRemoteEPCOpcode OpC, uint64_t SeqNo, ExecutorAddr TagAddr,
                 SimpleRemoteEPCArgBytesVector ArgBytes) override;
 
   Error waitForDisconnect();
 
   void handleDisconnect(Error Err) override;
 
+  ~SimpleRemoteEPCServer() override {
+    if (Error Err = waitForDisconnect())
+      ReportError(std::move(Err));
+  }
+
 private:
   Error sendMessage(SimpleRemoteEPCOpcode OpC, uint64_t SeqNo,
                     ExecutorAddr TagAddr, ArrayRef<char> ArgBytes);
 
   Error sendSetupMessage(StringMap<ExecutorAddr> BootstrapSymbols);
 
   Error handleResult(uint64_t SeqNo, ExecutorAddr TagAddr,
                      SimpleRemoteEPCArgBytesVector ArgBytes);